This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to collect prospective standardized data from participants to help better define the clinical phenotype of nondystrophic myotonias. The secondary aim is to establish clinically relevant endpoints for use in therapeutic trials.